1. Field of the Invention
The present invention relates to a method for measuring an object based on images obtained by plural cameras and a photographing apparatus used for the method.
2. Description of the Prior Art
Conventionally, a method is known in which an object is measured based on images captured by plural cameras to obtain three-dimensional information such as distance images of the object. Further, various photographing apparatuses for photographing such images are known.
In order to obtain three-dimensional information based on two images, extraction of corresponding points in the two images is required. However, since images captured by the conventional photographing apparatuses differ from each other in luminance, color balance or focus states in corresponding points, accurate extraction of corresponding points is difficult.
Japanese unexamined patent publication Nos. 2002-218506 and 2002-218507, for example, disclose a photographing apparatus in which a stereo adapter is attached to one optical system to obtain stereo images. According to this photographing apparatus, capture of images from two virtual viewpoints is possible in one optical system. However, the photographing apparatus cannot perform an AE (Auto Exposure) operation or an AWB (Auto White Balance) operation for each image individually. Thus, two images differ from each other in luminance or color balance in corresponding points, making accurate correspondence difficult.
In order to solve this problem, it is proposed that luminance in plane parts seen common to two images is compared to each other to correct a luminance value of the entire image (Japanese unexamined patent publication No. 2002-216125).
More specifically, according to the publication, luminance in regions common to two images is compared to each other to make correction to the image. However, it is intended to equalize luminance of images by making correction to the image after photographing, and therefore luminance of images cannot be equalized sufficiently depending on image states. Further, when images differ from each other in color balance or focus states, it is almost impossible to equalize color balance or focus states through correction. Accordingly, accurate correspondence is difficult and three-dimensional information with good degree of precision concerning an object cannot be obtained.    Related Patent Publication 1:
Japanese unexamined patent publication No. 2002-218506    Related Patent Publication 2:
Japanese unexamined patent publication No. 2002-218507    Related Patent Publication 3:
Japanese unexamined patent publication No. 2002-216125